1. Field of the Invention
The present invention regards a method of operation of a position measuring device.
2. Description of the Related Art
A method for the serial transmission of position data from a position measuring system to a downstream-connected evaluation unit, or electronic follow-up device, is known from EP 660 209 B1 of Applicant. In this case the bidirectional data transmission on a data line is synchronized with the aid of a phase signal of a defined transmission phase frequency on a parallel phase line. Along with an increase in the transmission of position data and possibly other data in this way, the demands regarding the transmission speed, or the amount of data to be transmitted, also increase. If now, besides the transmission speed, in addition the transmission distance between the position measuring system and the evaluation unit also increases, the result in the end are significant signal running times of the data transmitted on the data line. It is necessary to take into account the resulting delay times for the correct further processing of the various data. The reason for this is that on the part of the evaluation unit it is always necessary to provide a definite assignment of the data bits transmitted on the data line to the phase edges of the phase signal in order to assure the correct further processing of the various data. Thus, without further steps, clear limitations result with respect to maximally permissible transmission paths, or cable lengths, and the maximally permissible transmission speed, or transmission phase frequency. The correlation of the maximally permissible transmission phase frequency fC and the cable length LK is illustrated in FIG. 3. The graphic representation approximately indicates that with cable lengths of 100 m only a maximally permissible transmission phase frequency fC=500 kHz results.